The present invention relates to an exhaust gas recirculation system, and more particularly to a method and system for controlling the quantity of exhaust reentering a turbomachine after processing by a recirculation system.
The emissions from a turbomachine, such as a gas turbine, are closely regulated. There is a growing concern over the long-term effects of Nitrogen Oxides (hereinafter NOx), Carbon Dioxide (hereinafter “CO2”) and Sulfur Oxides (SOx) emissions on the environment. Operators of turbomachines desire methods of reducing the levels of NOx, CO2, and SOx emitted.
Significant amounts of condensable vapors exist in the exhaust gas stream. These vapors usually contain a variety of constituents such as water, acids, aldehydes, hydrocarbons, sulfur oxides, and chlorine compounds. Left untreated, these constituents will accelerate corrosion and fouling of the internal components if allowed to enter the turbomachine.
Exhaust gas recirculation (EGR) generally involves recirculating a portion of the emitted exhaust through an inlet portion of the turbomachine. The exhaust is then mixed with the incoming airflow prior to combustion. The EGR process facilitates the removal and sequestration of concentrated CO2, and may also reduce the NOx and SOx emission levels.
There are a few concerns about the currently known EGR systems. The rate and composition of the recirculated exhaust impacts the turbomachine operability including, but not limiting of: combustor stability, emissions, compressor stability, and component life.
For the foregoing reasons, there is a need for a method for controlling the composition of the inlet fluid exiting the EGR system. The method should control the rate of exhaust reentering the turbomachine using an open loop methodology.